In an effort to reduce the amount of pollution emissions from gas-powered turbines, governmental agencies have enacted numerous regulations requiring reductions in the amount of oxides of nitrogen (NOx) and carbon monoxide (CO). In response to these increasingly stringent emissions requirements, engine manufacturers have developed improved combustion systems. Lower combustion emissions can often be attributed to a more efficient combustion process, with specific regard to fuel injector location, airflow rates, and mixing effectiveness.
One type of improved combustion system for reducing emissions is a can-annular low NOx combustor. That is, the combustion system comprises a plurality of individual combustors arranged generally about a centerline of the gas turbine engine. Accordingly, each combustor receives a portion of the compressed air from the engine compressor, adds fuel from a fuel source, mixes the fuel and air together and ignites the mixture to produce hot combustion gases. These hot combustion gases then must pass from the individual combustors to the turbine inlet. Due to the geometry and orientation of the individual combustors, a plurality of individual ducts, also known as transition ducts, connect an outlet region of the combustor to the inlet region of the turbine. As such, the transition ducts also change geometry, generally from a cylindrical shape at its inlet (the combustor exit) to a semi-rectangular frame-like shape at its outlet (the turbine inlet). For reference to a transition duct exhibiting this geometry, see FIG. 1. As such, a plurality of transition ducts arranged about the gas turbine engine will result in their outlets each supplying a sector of the turbine inlet with the hot combustion gases from the individual combustors.
The transition ducts are typically located within a compressor discharge plenum, which is the region immediately downstream of the compressor of the engine. Compressed air is discharged into this plenum where it is then directed into the plurality of individual combustors. By locating the transition ducts in this plenum of air, the compressed air can also be used to cool the transition ducts prior to that air entering one or more of the individual combustors.
The transition ducts direct hot combustion gases to the turbine. However, the transition duct-to-turbine inlet region may leak hot combustion gases or restrict the flow of cooling air between adjacent transition ducts due to the geometry of the transition ducts and turbine inlet, dimensional tolerances and assembly techniques utilized. Therefore, in order to minimize any leakage, a seal arrangement is typically utilized at the region between the transition ducts and the turbine inlet. One type of seal of the prior art is a sheet metal plate that slides between adjacent transition ducts to prevent hot combustion gases from squeezing between adjacent transition ducts.
Another type of seal common in gas turbine transition ducts is a plurality of interlocking teeth at a side seal location of a transition duct aft frame, such as that disclosed by U.S. Pat. No. 6,619,915, which is hereby incorporated by reference. Such a configuration is depicted in FIG. 2. As the transition ducts increase in operating temperatures, the aft frame region tends to expand radially outward, thereby causing the plurality of teeth to engage with a plurality of teeth of an adjacent transition duct, to thereby form a seal between adjacent transition ducts.
The engagement of the plurality of teeth from adjacent side seal regions of transition ducts is intended to reduce the amount of hot combustion gases leaking from the transition duct, but not necessarily eliminate it. The plurality of teeth from adjacent transition ducts form a labyrinth seal. That is, the plurality of teeth are designed to close the gaps, when operating at an elevated temperature, and not contact each other, as shown in FIG. 3.
However, conditions have been known to occur where the side seal regions of adjacent transition ducts do in fact contact each other. This can be due to improper installation of the transition ducts or excessive amounts of thermal growth or movement between adjacent transition ducts. Contact between adjacent side seal regions can result in unwanted wear such as fretting to the seal teeth, which then permits the seal teeth to oxidize due to the lack of cooling air passing between the interlocking teeth. A representative example of the wear to the seal teeth is depicted in FIG. 4.
As a result of this unwanted wear, it is necessary to repair the teeth of the side seal region in order to continue using the transition duct. The most common repair technique for this area of the transition duct is a weld repair, such as a manual TIG weld using a nickel-based weld rod. Such weld repair processes require extensive repair time, special fixturing to reduce distortion from the localized heating during the welding process, profile correction, and re-machining of the seal teeth in order to return the seal teeth to original equipment conditions. Such repair processes are extremely labor intensive, especially for smaller amounts of wear to the seal teeth.
The present invention seeks to overcome the problems of the prior art design by providing an improved repair methodology that reduces repair time and cost.